Watershed models are powerful tools for simulating the effect of watershed processes and management on soil and water resources. However, no comprehensive guidance is available to facilitate model evaluation in terms of the accuracy of simulated data compared to measured flow and constituent values. Thus, the objectives of this research were to: (1) determine recommended model evaluation techniques (statistical and graphical), (2) review reported ranges of values and corresponding performance ratings for the recommended statistics, and (3) establish guidelines for model evaluation based on the review results and project-specific considerations; all of these objectives focus on simulation of streamflow and transport of sediment and nutrients. These objectives were achieved with a thorough review of relevant literature on model application and recommended model evaluation methods. Based on this analysis, we recommend that three quantitative statistics, Nash-Sutcliffe efficiency (NSE), percent bias (PBIAS), and ratio of the root mean square error to the standard deviation of measured data (RSR), in addition to the graphical techniques, be used in model evaluation. The following model evaluation performance ratings were established for each recommended statistic. In general, model simulation can be judged as satisfactory if NSE > 0.50 and RSR < 0.70, and if PBIAS + 25% for streamflow, PBIAS + 55% for sediment, and PBIAS + 70% for N and P. For PBIAS, constituent-specific performance ratings were determined based on uncertainty of measured data. Additional considerations related to model evaluation guidelines are also discussed. These considerations include: single-event simulation, quality and quantity of measured data, model calibration procedure, evaluation time step, and project scope and magnitude. A case study illustrating the application of the model evaluation guidelines is also provided.

Model Evaluation Guidelines for Systematic Quantification of Accuracy in Watershed Simulations

The Soil and Water Assessment Tool (SWAT) model is a continuation of nearly 30 years of modeling efforts conducted by the USDA Agricultural Research Service (ARS). SWAT has gained international acceptance as a robust interdisciplinary watershed modeling tool as evidenced by international SWAT conferences, hundreds of SWAT-related papers presented at numerous other scientific meetings, and dozens of articles published in peer-reviewed journals. The model has also been adopted as part of the U.S. Environmental Protection Agency (USEPA) Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) software package and is being used by many U.S. federal and state agencies, including the USDA within the Conservation Effects Assessment Project (CEAP). At present, over 250 peer-reviewed published articles have been identified that report SWAT applications, reviews of SWAT components, or other research that includes SWAT. Many of these peer-reviewed articles are summarized here according to relevant application categories such as streamflow calibration and related hydrologic analyses, climate change impacts on hydrology, pollutant load assessments, comparisons with other models, and sensitivity analyses and calibration techniques. Strengths and weaknesses of the model are presented, and recommended research needs for SWAT are also provided.

/pdf/the-soil-and-water-assessment-tool-historical-development-4e4d97tdfq.pdf

The Soil and Water Assessment Tool: Historical Development, Applications, and Future Research Directions

The Soil and Water Assessment Tool (SWAT) model is a continuation of nearly 30 years of modeling efforts conducted by the U.S. Department of Agriculture (USDA), Agricultural Research Service. SWAT has gained international acceptance as a robust interdisciplinary watershed modeling tool, as evidenced by international SWAT conferences, hundreds of SWAT-related papers presented at numerous scientific meetings, and dozens of articles published in peer-reviewed journals. The model has also been adopted as part of the U.S. Environmental Protection Agency's BASINS (Better Assessment Science Integrating Point & Nonpoint Sources) software package and is being used by many U.S. federal and state agencies, including the USDA within the Conservation Effects Assessment Project. At present, over 250 peer-reviewed, published articles have been identified that report SWAT applications, reviews of SWAT components, or other research that includes SWAT. Many of these peer-reviewed articles are summarized here according to relevant application categories such as streamflow calibration and related hydrologic analyses, climate change impacts on hydrology, pollutant load assessments, comparisons with other models, and sensitivity analyses and calibration techniques. Strengths and weaknesses of the model are presented, and recommended research needs for SWAT are provided.

Soil and Water Assessment Tool: Historical Development, Applications, and Future Research Directions, The

https://www.eawag.ch/fileadmin/Domain1/Abteilungen/siam/software/swat/thur.pdf

Modelling hydrology and water quality in the pre-alpine/alpine Thur watershed using SWAT

Thirty-three brothels in rural and small-town Nevada, which contain between 225 and 250 prostitutes, are legal or openly tolerated and strictly controlled by state statute, city and county ordinances, and local rules. Twenty-two of the brothels are in places with populations between 500 and 8,000, and the remaining eleven are in rural areas. The legal and quasi-legal restrictions placed on prostitutes severely limit their activities outside brothels. These restrictions in conjunction with historical inertia, perceived benefits of crime and venereal disease control, and the good image of madams contribute to widespread positive local attitudes toward brothel prostitution. Interactions between clients and prostitutes in brothel parlors are also restricted and limited to a few basic types which are largely determined by entrepreneurial philosophy. KEY WORDS : Nevada, Political geography, Prostitution, Restricted activity spaces.

ANNALS of the Association of American Geographers

Three watershed-scale hydrologic and nonpoint-source pollution models, all having the three major components
(hydrology, sediment, and chemical), were selected based on a review of eleven models (AGNPS, AnnAGNPS, ANSWERS,
ANSWERS-Continuous, CASC2D, DWSM, HSPF, KINEROS, MIKE SHE, PRMS, and SWAT) presented in a companion article.
Those selected were SWAT, a promising model for long-term continuous simulations in predominantly agricultural watersheds;
HSPF, a promising model for long-term continuous simulations in mixed agricultural and urban watersheds; and
DWSM, a promising storm event (rainfall) simulation model for agricultural and suburban watersheds. In this article, applications
of these three models, as reported and found in the literature, are reviewed and discussed. Seventeen SWAT, twelve
HSPF, and eighteen DWSM applications are compiled. SWAT and HSPF require a significant amount of data and empirical
parameters for development and calibration. DWSM has efficient physically (process) based simulation routines and therefore
has a small number of calibration parameters. SWAT and HSPF were found suitable for predicting yearly flow volumes,
sediment, and nutrient loads. Monthly predictions were generally good, except for months having extreme storm events and
hydrologic conditions. Daily simulations of extreme flow events were poor. DWSM reasonably predicted distributed flow hydrographs,
and concentration or discharge graphs of sediment, nutrient, and pesticides at small time intervals resulting from
rainfall events. Combined use of these complementary models and perhaps other models having different strengths is warranted
to adequately address water quantity and quality problems and their solutions.

Watershed-scale hydrologic and nonpoint-source pollution models: review of applications

At present, there are over 34,000 impaired waters and over 58,000 associated impairments officially listed in the
U.S. Nutrients and sediment are two of the most common pollutants included in the list. States are required to identify and
list those waters within their boundaries that are not meeting standards, to prioritize them, and to develop Total Maximum
Daily Loads (TMDLs) for the pollutants of concern. Models are used to support development of TMDLs, typically to estimate
source loading inputs, evaluate receiving water quality, and determine source load allocations so that receiving water quality
standards are met. Numerous models are available today, and selection of the most suitable model for a specific TMDL project
can be daunting. This article presents a critical review of models simulating sediment and nutrients in watersheds and
receiving waters that have potential for use with TMDL development and implementation. The water quality models
discussed, especially those with sediment and/or nutrient components, include loading models (GWLF and PLOAD),
receiving water models (AQUATOX, BATHTUB, CE-QUAL-W2, QUAL2E, and QUAL2K), and watershed models having
both loading and receiving components (AGNPS, AnnAGNPS, CASC2D/GSSHA, DWSM, HSPF, KINEROS2, LSPC, MIKE
SHE, and SWAT). Additional models mentioned include another receiving water quality model (WASP), watershed models
(ANSWERS storm event, ANSWERS continuous, PRMS storm event, SWMM, and WEPP), and BMP models (APEX, REMM,
and VFSMOD). Model sources, structures, and procedures for simulating hydrology, sediment, and nutrients are briefly
described for the reviewed models along with an assessment of their strengths, limitations, robustness, and potentials for using
in sediment and/or nutrient TMDLs. Applications of AGNPS, APEX, BATHTUB, CE-QUAL-W2, GWLF, and SWAT in TMDL
developments are presented. Applications of some of the other models (DWSM, GSSHA, and KINEROS2) relevant to TMDL
studies are also presented. The models proved to be useful; however, they require a learning process. Simple models are easy
to use but have limitations; comprehensive models are labor and data intensive but offer extensive analysis tools. Finally,
recommendations are offered for advancing the sediment and nutrient modeling technologies as applied to TMDL
development and implementation. Advances could be made towards: making the best use of existing models, enhancing the
existing models, combining strengths of existing models, developing new models or supplemental components with physically
based robust routines, numerous field applications, sensitivity analyses, full documentation, and rigorous education and training.

/pdf/sediment-and-nutrient-modeling-for-tmdl-development-and-38pk5js1g1.pdf

Sediment and nutrient modeling for tmdl development and implementation

Flow and concentrations of suspended sediment, nitrate–N, phosphate–P, atrazine, and metolachlor were
monitored during the spring seasons of 1998 and 1999, primarily during storm events, at a tributary station (Big Ditch) and
two main–stem stations (Fisher and Mahomet) of the Upper Sangamon River watershed in east central Illinois. These three
stations respectively drain 98, 622, and 932 km2 of mainly agricultural lands. Rainfall data were collected from six newly
established raingage stations. The study provides a valuable database to understand some of the complex physical and
chemical processes in an east central Illinois watershed and to calibrate, validate, and evaluate mathematical models.
Analyses of the limited data from different sampling methods showed consistencies among the methods. The nitrate–N
concentrations in Big Ditch during intense storms of 1998 showed inverse relationships with water discharge. Higher
goodness–of–fit of the relationships was found within the data for individual months than for the combined set, showing
dependence on varying climate, land cover, and management practices during the growing season. The nitrate–N
concentrations at each of the three stations during less intense storms in 1999 showed weak positive relationships with water
discharge. The total nitrate–N load in Big Ditch generated by the storms of March, May, and June of 1998 was similar to the
average annual load, indicating the importance of single–event storms, and therefore their need for close attention. After the
intense storm of April 1999, the less intense storms during May and June after long low–flow periods significantly raised the
nitrate–N concentrations in all three stations. A similar pattern was noticed in the 1998 observations before each of the major
peaks, when the smaller peaks elevated nitrate–N concentrations followed by dilution with the larger peaks. Results of this
study show positive relationships between suspended sediment concentration and water discharge for the smaller watershed
(Big Ditch); however, no relationships were found in the larger watersheds (Upper Sangamon River at Fisher and Mahomet).
Observed data at each of the stations showed positive relationships of phosphate–P, atrazine, and metolachlor concentrations
with water discharge.

/pdf/water-sediment-nutrient-and-pesticide-measurements-in-an-33sbr4s17f.pdf

Water, sediment, nutrient, and pesticide measurements in an agricultural watershed in illinois during storm events

Based on recent reviews of 11 physically based watershed models, the long-term continuous model soil and water assessment tool (SWAT) and the storm event dynamic watershed simulation model (DWSM) were selected to examine their hydrologic formulations, calibrate, and validate them on the 620 km2 watershed of the upper Little Wabash River at Effingham, Ill., and examine their compatibility and benefits of combining them into a more comprehensive and efficient model. Calibration and validation of the SWAT by comparing monthly simulated and observed flows and adjusting the model-assigned resulted in coefficients of determination and Nash–Sutcliffe coefficients for individual years and cumulatively for the calibration period (1995–1999) and for the entire simulation period (1995–2002) mostly above or near 0.50 with an exception of 0.05 and −0.27 , respectively, in 2001, relatively a dry year. Visual comparisons of the hydrographs showed SWAT’s weakness in predicting monthly peak flows (mostly underpredictions....

/pdf/storm-event-and-continuous-hydrologic-modeling-for-2alzcpcz27.pdf

Deva K. Borah

Papers

Watershed-scale hydrologic and nonpoint-source pollution models: review of applications

Sediment and nutrient modeling for tmdl development and implementation

Water, sediment, nutrient, and pesticide measurements in an agricultural watershed in illinois during storm events

Storm Event and Continuous Hydrologic Modeling for Comprehensive and Efficient Watershed Simulations

DWSM - a Dynamic Watershed Simulation Model.